Improvement of Activated Sludge Process Using a Nonlinear PI Controller Design via Adaptive Gain

Abstract

Abstract The goal of this work was to design an adaptive nonlinear proportional–integral (PI) controller to regulate the dynamics of an aerobic wastewater bioreactor, providing a mathematical sketch of proof of the convergence of the control scheme. Adequate operating regions were determined and the corresponding steady-state points were studied via phase portrait and bifurcation analysis. The proposed controller was applied to a wastewater treatment plant to regulate dissolved oxygen (DO) concentration and, indirectly, the concentration of chemical oxygen demand (COD) in the bioreactor; the recirculation flow rate was considered as the manipulated variable. The implementation was based on the mathematical bioreactor’s model, which was experimentally verified; it describes COD dynamics, DO, biomass, recirculation biomass concentrations, and temperature. The obtained results, via numerical simulations, showed that the proposed control law is able to control DO concentration; this control exhibited better performance in comparison to a linear one.